Spray guns with vibrating armature drives typically have a piston which is movable in a pump cylinder, is urged toward one position by a tension spring to suck in liquid and can be shifted against the force of the tension spring by an electromagnet to convey the sucked-in liquid to a spray head of the spray gun. The pump piston, the armature of the electromagnet and the tension spring together form a system capable of vibrating in response to energy supplied continuously thereto from an a.c. voltage network during spraying of the liquid.
In these known spray guns, it is possible to adjust the spray output, namely, the amount of liquid which is sprayed per unit of time, by limiting the suction stroke of the pump piston with an adjustable mechanical stop. In this manner, however, the spray output can only be reduced to approximately 300 g/min., since a further reduction of the piston suction stroke will cause the liquid to be no longer satisfactorily sprayed.
The purpose of the present invention is to provide a method and a circuit for operating a spray gun having a vibrating armature drive which assures good spraying of the liquid even in the case of a small spray output.